spaceship/audio/Sfx.gd

class_name Sfx
extends RefCounted

# Forgejo #146: the three things that happen to something and should be
# heard - a shot leaving a gun, a vessel dying, a structure coming down.
#
# The sounds themselves are synthesised (see audio/make_sfx.py) rather than
# downloaded. The ticket asked for free sources and the good ones are in its
# comments, but a generated sound has no licence to track, no attribution to
# keep, and no binary in the repository whose provenance nobody can check
# later. Swapping in a file from one of those packs is a matter of replacing
# the .wav - nothing here knows or cares which it is.
#
# Parented to the tree root for the same reason Music is: a sound started by
# something that is about to be freed - which is every one of these, a dying
# ship being the obvious case - cannot live on the thing that started it.
#
# A POOL rather than one player, because these overlap constantly: a fleet
# firing is several shots inside one shot's length. The oldest is recycled
# when they are all busy, which is the right thing to lose.

const NODE_NAME: String = "SfxPlayers"
const VOICES: int = 12

const SHOT: String = "shot"
const SHIP_DEATH: String = "ship_death"
const ENEMY_DEATH: String = "enemy_death"
const BUILDING_DEATH: String = "building_death"
const DIALOG: String = "dialog"
const BOSS_SCREAM: String = "boss_scream"
# #210, #213, #214, #208.
const PICKUP: String = "pickup"
const ASTEROID_BREAK: String = "asteroid_break"
const GAS_BLAST: String = "gas_blast"
const BLACK_HOLE: String = "black_hole"

# PRELOADED, not paths. play() used to load() on every call, which is a
# cache hit after the first time but a synchronous disk read and decode the
# first time - on the frame the sound was asked for. Ten sounds meant ten
# occasional late starts, one per sound, which is what "sometimes starting a
# bit late" was. Swapping in a different file is still just replacing the
# .wav; nothing here knows or cares which it is.
const SOUNDS: Dictionary = {
	SHOT: preload("res://audio/sfx_shot.wav"),
	SHIP_DEATH: preload("res://audio/sfx_ship_death.wav"),
	ENEMY_DEATH: preload("res://audio/sfx_ship_death.wav"),
	BUILDING_DEATH: preload("res://audio/sfx_building_death.wav"),
	DIALOG: preload("res://audio/sfx_dialog.wav"),
	BOSS_SCREAM: preload("res://audio/sfx_boss_scream.wav"),
	PICKUP: preload("res://audio/sfx_pickup.wav"),
	ASTEROID_BREAK: preload("res://audio/sfx_asteroid_break.wav"),
	GAS_BLAST: preload("res://audio/sfx_gas_blast.wav"),
	BLACK_HOLE: preload("res://audio/sfx_black_hole.wav"),
}

# Per-sound level. A shot is fired constantly and a death happens once, so
# they cannot share a volume and stay in proportion.
const LEVELS: Dictionary = {
	SHOT: -26.0,
	SHIP_DEATH: -23.0,
	ENEMY_DEATH: -23.0,
	BUILDING_DEATH: -23.0,
	DIALOG: -19.0,
	BOSS_SCREAM: -13.0,
	# Quieter than everything else by a clear margin: it is the only sound
	# here that can happen several times a second for minutes at a time, and
	# a pickup blip at shot volume would be the loudest thing in the game.
	PICKUP: -32.0,
	ASTEROID_BREAK: -24.0,
	GAS_BLAST: -21.0,
	# The prologue's one irreversible moment, and nothing else is playing
	# under it.
	BLACK_HOLE: -11.0,
}

# Shots vary a little in pitch so a stream of them does not turn into one
# flat machine-gun note. The deaths do not: they are events, and a wobbling
# explosion sounds broken rather than varied.
const SHOT_PITCH_SPREAD: float = 0.12
# Pickups repeat harder than shots do, so they vary too - but less, because a
# pickup is a short bright tone and a wide spread on one reads as wrong notes
# rather than as variety. Rocks also break in twos and threes.
const PITCH_SPREAD: Dictionary = {
	SHOT: SHOT_PITCH_SPREAD,
	PICKUP: 0.07,
	ASTEROID_BREAK: 0.09,
}


# Builds the voice pool before anything needs it. _pool() is lazy, so without
# this the first sound in a session paid for twelve AudioStreamPlayer nodes
# being created on the frame it was asked for - the worst late start of all,
# and the one that happens every session.
static func warm(tree: SceneTree) -> void:
	if tree == null:
		return
	# Deferred, like Music.ensure(): this is called from _ready(), where the
	# parent is still setting up children and a direct add_child() is
	# refused outright. The lazy path in play() runs during an ordinary
	# frame and does not need it.
	var build: Callable = func() -> void:
		_pool(tree)
	build.call_deferred()


static func _pool(tree: SceneTree) -> Node:
	var existing: Node = tree.root.get_node_or_null(NODE_NAME)
	if existing != null:
		return existing
	var pool := Node.new()
	pool.name = NODE_NAME
	# #128 stops the tree for dialogs. A sound already in flight should
	# finish rather than freeze mid-bang.
	pool.process_mode = Node.PROCESS_MODE_ALWAYS
	tree.root.add_child(pool)
	for i in range(VOICES):
		var voice := AudioStreamPlayer.new()
		voice.process_mode = Node.PROCESS_MODE_ALWAYS
		pool.add_child(voice)
	return pool


# Plays one sound. Safe from a node on its way out of the tree, and safe to
# call far more often than there are voices.
static func play(tree: SceneTree, id: String) -> void:
	if tree == null or not SOUNDS.has(id):
		return
	var stream: AudioStream = SOUNDS[id] as AudioStream
	if stream == null:
		return
	var pool: Node = _pool(tree)
	var voice: AudioStreamPlayer = null
	for child in pool.get_children():
		if not (child as AudioStreamPlayer).playing:
			voice = child
			break
	if voice == null:
		# All busy. The oldest is the one furthest through its own sound, so
		# it is the one with the least left to lose.
		var most: float = -1.0
		for child in pool.get_children():
			var at: float = (child as AudioStreamPlayer).get_playback_position()
			if at > most:
				most = at
				voice = child
	if voice == null:
		return
	voice.stream = stream
	voice.volume_db = float(LEVELS.get(id, -10.0))
	var spread: float = float(PITCH_SPREAD.get(id, 0.0))
	voice.pitch_scale = 1.0 if spread <= 0.0 else 1.0 + randf_range(-spread, spread)
	voice.play()